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Case study · Education · Wood dust
A secondary school design and technology department asked us to examine the dust extraction on its workshop machines. Most of the system controlled dust well - but two capture points did not, and in a room full of teenagers that matters. Here is what we tested, what we found, and how it was put right.
The site
The workshop sits at the heart of a large secondary school's design and technology provision. On a normal day it runs full classes of pupils cutting, drilling and finishing timber and sheet material, supervised by teaching staff and a workshop technician who is in the room far more hours than anyone else.
Five extraction points were in scope. A cross-cut saw and a pillar (bench) drill each had their own local capture; a disc and belt sander had a hood behind the abrasive; and a wheeled shop-vac served the hand-held power tools and the general clean-down. A small high-level extract dealt with the finishing bay. Between them they are meant to keep wood dust out of the breathing zone of thirty-odd people at a time.
The school had done the right thing in having the machines ducted at all - plenty of older workshops still rely on a brush and an open window. The question the examination answers is a harder one: is each of those capture points actually moving enough air, in the right place, to control the dust it was fitted to control?
The hazard and the law
It is easy to think of sawdust as harmless because it is familiar. It is not. Hardwood dust is classified as capable of causing cancer - most often of the nose and nasal sinuses - and both hardwood and softwood dust are leading causes of occupational asthma. The Health and Safety Executive sets workplace exposure limits of 3 mg/m³ for hardwood dust and 5 mg/m³ for softwood dust, each as an 8-hour time-weighted average, and where the two are mixed the lower hardwood figure covers the whole mixture.
In a school, two things make this sharper. First, the exposure is repeated: a technician can spend a career in the same room, and pupils pass through for years. Second, the law gives no discount for being an educational setting. Where extraction is provided to control a substance hazardous to health, Regulation 9 of COSHH requires it to be thoroughly examined and tested at least every 14 months by a competent person, with the record kept. The workshop's dust extraction is that control, and the 14-month clock applies to it.
What we tested
We examined and tested all five points individually. At each machine we measured the capture velocity at the point where dust is generated - the saw blade, the drill table, the abrasive face - because that is where control either works or fails. A good reading at the hood mouth means little if the air is not fast enough where the cutting actually happens. We also inspected the ductwork for leaks and blockages, checked the fan, examined the filter condition on the shop-vac, and looked for airflow indicators that would let staff see at a glance whether a machine's extraction is working before they switch it on.
The benchmark for small woodworking machines is a capture velocity in the region of 1 to 2 m/s at the source for fine, light dust, with duct transport velocities high enough - commonly around 15 to 20 m/s - to keep the dust moving and stop it settling in the ducts. Each point was judged against the benchmark appropriate to it, and a qualitative check confirmed whether visible dust was actually being drawn away or escaping into the room.
What we found
The cross-cut saw, the bench drill and the finishing-bay extract all performed to benchmark - good capture at source, clean ducting, fans running true. The problems were at the two points that handle the finest dust of all.
| Capture point | Benchmark | Measured | Result |
|---|---|---|---|
| Cross-cut saw hood | Capture at blade | Good capture, clean duct | Pass |
| Pillar (bench) drill | Capture at table | Within benchmark | Pass |
| Disc / belt sander hood | Capture behind abrasive | Weak - dust escaping to the front of the belt | Fail |
| Shop-vac (hand tools) | Rated suction / M-class filtration | Suction well down - filter blinded with fine dust | Fail |
| Finishing-bay extract | General extract | Within benchmark | Pass |
The sander told the familiar story: fine abrasive dust is the hardest of all to capture, and the hood had been designed - or positioned - to catch coarse debris rather than the respirable cloud that sanding actually throws forward. The shop-vac had simply been run until its filter was choked, so its measured suction had collapsed and it was recirculating fine dust rather than capturing it. Neither machine carried an airflow indicator, so nobody using them had any way of knowing control had been lost.
The remedial actions
A report that only says "fail" is half a job. Ours set out exactly what to do at each failed point, ranked by risk, so the department could act without going back and forth:
The outcome
With the sander hood modified, the shop-vac filter replaced and airflow indicators fitted, the two failed points were re-tested and met their benchmarks. The workshop now has a complete, dated record showing control at every machine, the technician and pupils are no longer breathing the fine dust those two points had been leaking, and the department knows precisely when the next 14-month examination falls due.
The lesson is not that this school was careless - it had ducted its machines and brought us in. It is that extraction quietly degrades. Filters blind, hoods get nudged out of position, and the finest dust - the dust that matters most for health - is the first thing a tired system stops catching. A machine can look and sound as though it is working while controlling almost nothing. Only measurement at the source tells you the truth, which is exactly why the 14-month examination exists. For a design and technology department, booking it into a holiday and budgeting for a little remedial work is the difference between a workshop that looks safe and one that is.
Sources and further reading
The duties, exposure limits and control standards described here come from the Health and Safety Executive. For your own process, always work from the current HSE guidance:
Questions
Yes. Wherever woodworking machines are fitted with dust extraction to control exposure, that extraction is local exhaust ventilation and must have a thorough examination and test (TExT) under Regulation 9 of COSHH at least every 14 months, with a record kept. A school is an employer like any other and the duty applies to it in full, with the added point that children are present.
Because wood dust is a genuine health hazard, not just a nuisance. Hardwood dust can cause cancer, particularly of the nose, and both hardwood and softwood dust cause occupational asthma. The workplace exposure limits are 3 mg/m³ for hardwood and 5 mg/m³ for softwood as 8-hour averages; where the two are mixed, the 3 mg/m³ figure applies to all of it. Pupils and the workshop technician are exposed repeatedly over years.
We measure the capture or face velocity at each machine's hood or extraction point - the air speed that pulls dust away from the cutter before it reaches the person - and compare it with the benchmark for that machine. We inspect the ductwork, fan and filter, check that airflow indicators are fitted and working, and carry out a qualitative check of capture at the tool.
No. Each capture point is assessed on its own merits, so a report can read as a pass on some machines and a fail on others. That is useful: it tells you exactly which points to put right rather than condemning the whole workshop. The failed points must be corrected and re-tested before they are relied on again.
That is a judgement for the school's risk assessment, informed by the report. Often the machines that passed can continue in use while the failed points are taken out of service or restricted until fixed. The report sets out the risk at each point so the department can make that call with the facts in front of it.
At least every 14 months under COSHH, and sooner if the system is altered, a machine is added, or something changes that could affect control. Many schools align the test with a summer holiday so any remedial work can be done while the workshop is empty.
Tell us your capture points and the process they control, and we will quote the thorough examination and test to COSHH and HSG258.
